Inkjet printing systems use pigment-based inks and dye-based inks. There are advantages and disadvantages with both these types of ink. For example, in dye-based inks the dye particles are dissolved in liquid and the ink therefore tends to soak into the paper more. This makes the ink less efficient and can reduce the image quality as the ink bleeds at the edges of the image. Methods for overcoming this problem include drying the ink more quickly when it is applied to the paper, using harder paper, and using special coatings on the paper.
In pigment-based inks, the pigment particles are larger and remain in suspension rather than dissolving in liquid. This helps pigment inks remain more on the surface of the paper rather than soaking into the paper. Pigment ink is therefore more efficient than dye ink because less ink is needed to create the same color intensity in a printed image. Pigment inks also tend to be more durable and permanent than dye inks. For example, pigment inks smear less than dye inks when they encounter water.
One drawback with using pigment-based inks in an inkjet system, however, is the out-of-box performance of the inkjet printheads after shipping and prolonged storage of inkjet pens. Inkjet pens have a printhead affixed at one end which is internally coupled to a supply of ink. The ink supply may be self-contained within the pen body or it may reside on the printer outside of the pen and be coupled to the printhead through the pen body.
Pigment inks consist of an ink vehicle and high concentrations of insoluble pigment particles typically coated with a dispersant that enables the particles to remain suspended in the ink vehicle. Over long periods of storage of an inkjet pen, gravitational effects on the large pigment particles and/or degradation of the dispersant can cause pigment settling or crashing, which can impede or completely block ink flow to the firing chambers and nozzles in the printhead. The result is poor out-of-box performance by the printhead and reduced image quality. In dye-based inks the dye particles are more fully dissolved in liquid, so this problem is mostly avoided.